The present invention relates to a rolling bearing for use in information equipment, acoustic/video equipment and so on, and a retainer for the same. In particular, the present invention relates to a rolling bearing suitable for use in a magnetic disk apparatus (HDD) and an optical disk apparatus, and a retainer for the same.
Conventionally, grease lubrication of a rolling bearing is executed by applying grease to a rolling body or one or more pockets formed in a retainer, or by applying grease into raceway grooves formed in the inner and outer rings of the rolling bearing. In addition, there is also employed a method in which grease is previously placed on one end surface of a circular ring constituting a retainer of a rolling bearing. In this method, when the rolling bearing is rotated, the grease, which is dropped down from the end surface due to the centrifugal force thereof, can be supplied to the raceway grooves of the inner and outer rings.
In the method of applying grease into the raceway grooves, in case where the quantity of grease is excessively large, torque is increased, torque is varied, or an acoustic characteristic is worsened. In case where the quantity of grease is reduced so as to avoid the above problem, lubrication by the grease is insufficient. On the other hand, in case where the method of loading grease into the raceway grooves is combined with the method of placing grease on one end surface of a circular ring forming a retainer, even when the quantity of grease to be applied into the raceway grooves is reduced, the rolling bearing can be lubricated sufficiently by the grease.
On the other hand, in the case of a rolling bearing requiring low torque and low torque variation, oil lubrication is employed. As a method for applying lubrication oil into a rolling bearing, there are known a method of applying lubrication oil into the raceway grooves of the inner and outer rings of the rolling bearing, and a method in which inner and outer rings are immersed in liquid composed of lubricating oil and solvent dissolved in the lubricating oil and, after then, the solvent is evaporated.
However, referring to the grease lubrication of a rolling bearing, in the method of placing grease on one end surface of a circular ring forming a retainer, since the grease is dropped down during the rotation of the rolling bearing, there is a fear that torque, Non-Repeatative-Runout Oscillation (hereinafter abbreviated to xe2x80x9cNRROxe2x80x9d), and the rotation frequency (vibration fc) of the retainer can vary irregularly. Therefore, even in case where this method is combined with the method of loading grease into the raceway grooves, as a method for grease-lubricating a rolling bearing that is used especially in a magnetic disk apparatus (HDD) and an optical disk apparatus and is rotated at a high speed, there is still room for improvement.
Also, in the above-mentioned lubricating oil loading method, especially, since the lubricating oil having a low viscosity is hard to be held in the rolling bearing, in order to obtain good lubricating property for a long period of time, it is necessary to continue to supply the lubricating oil from outside. In case where lubricating oil having a high viscosity is used, the lubricating oil can be held for a longer period of time within the rolling bearing. However, in this case, there arises another problem that torque increases.
The present invention aims at eliminating the drawbacks found in the above-mentioned conventional grease lubricating methods. Accordingly, it is an object of the invention to be able to lubricate properly a rolling bearing for use in a magnetic disk apparatus (HDD) and an optical disk apparatus to be rotated at a high speed according to a method of placing grease on one end surface of a circular ring forming a retainer. Also, it is another object of the invention to be able to obtain good lubrication property for a long period of time even in case where lubricating oil is not supplied from outside.
The above object can be achieved by a retainer for use in a rolling bearing, according to the present invention, the retainer comprising a circular ring having an end surface on which a plurality of pockets are formed at predetermined intervals along a circumferential direction of the circular ring. Each of the pockets is formed by a projecting portion projected from the end surface, and a recessed portion recessed from the end surface. Each of the pockets includes a pocket surface including an inner surface of the projecting portion and a concave surface of the recessed portion. The end surface has a grease placement portion that is disposed between mutually adjoining ones of the pockets. The circular ring comprises a first groove for connecting together the grease placement portion and the pocket surface.
In the above-mentioned retainer, the circular ring may further comprise:
a wall portion projecting from the end surface, the wall portion extending along the circumferential direction and disposed between the mutually adjoining ones of the pockets.
In the above-mentioned retainer, the circular ring may further comprise:
a lubricant storing cavity disposed between the mutually adjoining ones of the pockets; and
a second groove for connecting the lubricant storing cavity and the pocket surface.
In the above-mentioned retainer, it is advantageous that the first groove and the groove extend along the circumferential direction and are aligned with each other.
In the above-mentioned retainer, it is advantageous that the circular ring further comprises:
first and second lubricant storing cavities disposed between the mutually adjoining ones of the pockets;
a second groove for connecting the first lubricant storing cavity and the pocket surface of one of the mutually adjoining one; and
a third groove for connecting the second lubricant storing cavity and the pocket surface of the other one of the mutually adjoining ones.
In the above-mentioned retainer, it is advantageous that the width of the first groove is set such that, in the circumferential direction of the circular ring, it becomes narrower as it approaches the pocket surface and it becomes narrower as the depth of the groove from the grease placement surface increases.
The above-mentioned object can also be attained by a rolling bearing, according to the other aspect of the present invention, comprising a retainer according to the above-mentioned aspect of the present invention.
According to the present retainer, in case where the present retainer is incorporated into a rolling bearing and is then rotated, the grease placed on the placement surface moves toward the pocket surface through the groove for connecting together the placement surface and pocket surface directly, and the base oil of the grease is supplied from the pocket through the rolling body to raceway grooves formed in the inner and outer rings of the rolling bearing. Also, due to the existence of the wall portion, during rotation, drop-down of the grease from the placement surface due to its own centrifugal force can be prevented.
Also, according to the invention, there is provided a retainer for use in a rolling bearing structured such that, on one end surface of a circular ring disposed concentrically with a shaft, there are formed a plurality of pockets at given intervals along the circumferential direction of the circular ring, each of the pockets is formed of a projecting portion formed so as to project from the above end surface and a recessed portion formed so as to be recessed from the end surface, each pocket includes a pocket surface composed of the inner surface of the projecting portion and the concave surface of the recessed portion, and the retainer is used with grease placed between the mutually adjoining ones of the pockets on the end surface, wherein, in the circular ring, there is formed, between the mutually adjoining ones of the pockets on said end surface, a cavity into which lubricant (or lubricating oil) can be loaded, and, there is also formed a groove for connecting together the cavity and the pocket surface directly.
In the case of the present retainer, it is incorporated into a rolling bearing with lubricant loaded into the cavity; and, the lubricant within the cavity moves toward the pocket surface through the groove for connecting together the cavity and the pocket surface directly, and lubricating oil (in the case of grease, the base oil of the grease) is supplied from the pocket through the rolling body to the raceway grooves formed in the inner and outer rings of the rolling bearing. Thanks to this, even in case where lubricating oil is not supplied from outside, there can be obtained a good lubricating property for a long period of time.
In the retainer according to the invention, preferably, the width of the groove may be set such that, in the circumferential direction of the circular ring, it becomes narrower as it approaches the pocket surface and it becomes narrower as the depth of the groove from the placement surface increases.
Further, according to the other aspect of the invention, there is provided a rolling bearing including a retainer according to the above-mentioned aspect of the invention.